Keller's earliest editing work includes the Academy Award-nominated films The Five Pennies (1959), Pocketful of Miracles (1961), and Come Blow Your Horn (1963). He earned his first Eddie Award nomination from American Cinema Editors (ACE, of which he was a member) for his work on A Pocketful of Miracles. In addition, he was the editor for the comic films Papa's Delicate Condition (1963, starring Elisha Cook, Jr. and Laurel Goodwin) and For Those Who Think Young (1964, starring James Darren). He also edited the science fiction film Cyborg 2087 (featuring Byron Morrow and Warren Stevens) and the 26th Tarzan franchise film, Tarzan and the Valley of Gold (starring Nancy Kovack and David Opatoshu), both released in 1966.

Keller earned his first Academy Award (or Oscar) nomination in Best Film Editing for the 1967 war drama Beach Red (he also received an Eddie Award nomination for this film). His next Oscar nomination, for the following year's Bullitt (featuring Ed Peck and Vic Tayback), resulted in his first and only win. Keller also received a BAFTA (British Academy of Film and Television Arts) Award nomination and won an Eddie Award for his editing work on Bullitt.

Following his success on Bullitt, Keller would reunite several more times with that film's director, Peter Yates. His work on Yates' 1972 comedy The Hot Rock (featuring Graham Jarvis) earned Keller his third Oscar nomination. Keller's other collaborations with Yates include John and Mary (1969, with cinematography by Gayne Rescher), For Pete's Sake (1974, starring Michael Sarrazin and featuring Ed Bakey and Vincent Schiavelli), and Mother, Jugs & Speed (1976, featuring Bruce Davison).

Keller received Eddie Award nominations for the pilot episode of the TV series Room 222 and for the 1972 TV movie Gargoyles (featuring Bernie Casey and Vic Perrin). He received his fourth and final Academy Award nomination, as well as his last Eddie Award nomination, for the 1973 drama Jonathan Livingston Seagull. After editing the films Beyond Reason (starring Diana Muldaur, with cinematography by John A. Alonzo) and Rolling Thunder, Keller died on Christmas Day, 1977, in Hollywood, California, at the age of 64.